The three, who deny any wrongdoing and have referred themselves to the standards watchdog, were caught in an undercover sting by Sunday Times reporters posing as lobbyists working for a fake energy firm.

In what one shadow cabinet minister called "a new low for British politics" that would "sicken" voters, the release of video footage of the exchanges further fuelled a Westminster controversy ignited by similar accusations against MP Patrick Mercer on Friday.

It forced ministers to insist they were serious about taking forward promised reforms such as a statutory register of lobbyists and "recall" powers to allow constituents to force out MPs guilty of serious breaches. And there were also calls for wider reforms to the House of Lords, including the expulsion of peers jailed for criminal offences.

Announcing the suspension of Lords Cunningham and Mackenzie pending the results of a probe, a Labour spokesman said it expected "the highest standards of its representatives and believes that they have a duty to be transparent and accountable at all times."

Lord Laird resigned the Ulster Unionist whip following a conversation with party leader Mike Nesbitt, who said it "expects and demands high standards of our elected representatives". The Northern Irish peer is also alleged to have discussed a £2,000 a month deal with a separate set of undercover reporters, this time from the BBC's Panorama and the Telegraph posing as lobbyists seeking the end of Fiji's suspension from the Commonwealth.

That is the same sting which led to Mr Mercer dramatically quitting the Tory whip, referring himself to the Commons sleaze watchdog and announcing he would quit the Commons in 2015. It is claimed the Newark MP was paid £4,000 by the bogus lobbying firm and tabled parliamentary questions and a motion, offered a security pass and set up an all-party parliamentary group on Fiji. Mr Mercer has referred his case to the Parliamentary Commissioner for Standards and is taking legal advice.

Lord Cunningham is alleged to have offered to ask parliamentary questions on behalf of the firm and take concerns directly to the Prime Minister. Recordings appear to show him asking for £12,000 a month rather than the offered £10,000 and telling the bogus lobbyists that he offered "value for money" because of his access to senior figures. But the peer, an MP for 22 years who served in Tony Blair's cabinet, insisted he had been testing his suspicions that he was being targeted by a scam.

The House of Lords code of conduct says peers must not act as paid advocates and "must not seek to profit from membership of the House by accepting or agreeing to accept payment for providing parliamentary advice or services".